function getRandomString() {
	return getDateFormatString() + getRandomNum(2);
}

// if the random string length is pow(2, digit)
function getRandomNum(digit) {
	var result = 0;
	for(var i = 1; i <= digit; i ++) {
  		result += Math.round(Math.random() * Math.pow(10, Math.pow(2, i)));
	}
	return result.toString();
}

function getDateFormatString() {
	var now = new Date();
	var year = now.getFullYear();
	var month = now.getMonth() + 1;
	var day = now.getDate();
	var hour = now.getHours();
	var min = now.getMinutes();
	var sec = now.getSeconds();
	return year.toString() + month.toString() + day.toString() + hour.toString() + min.toString() + sec.toString();
}